Clutches are used to control transmittal of torque in vehicles. In a vehicle having an automatic transmission, for example, multiple clutches are used to engage or disengage selected gearsets in real time to obtain desired gear ratios. Clutches used for this purpose generally include a plurality of rotatable friction discs employed as drive members internally splined to and axially moveable on a rotatable hub. A case or housing is coaxially aligned with the hub and supported for rotation independently of the hub. Driven reaction or pressure or plates are externally splined to the housing, and are interposed between the friction discs to form rotatable drive and driven elements alternately arranged on a common axis. The friction discs generally include a friction material layer on one or both sides of the plates. An actuator, including a hydraulic piston, may be adapted to apply a piston force to press the drive and driven elements into engagement, thereby permitting torque to be transferred from the hub to the housing.
It has been known how to provide dual gain capability with respect to friction disc and pressure plate clutch structures. For example, U.S. Pat. No. 6,227,340 B1 discloses a hydraulic fluid operated friction coupling comprising a multiple friction disc assembly. The multiple friction disc assembly includes a single piston actuator, and has first and second springs operatively configured and arranged in response to pressurization of the piston actuator to selectively engage first and second sets of plates and friction components, called clutch packs, for varying the gain of the coupling. Two separate Belleville springs are employed with the clutch packs, including one interposed between the two axially arranged clutch packs employed. The elimination of one of those relative bulky spring structures could facilitate use of shorter axial dimensions for such friction couplings, as those skilled in the art may appreciate.